Originally posted by jeffkrol Olympus is probably the compatibility champ with is short registration distance.
Canon is close though I suspect.
Canon EOS film and digital SLRs can, on the other hand, accept almost anything BUT a Canon FD lens with adapters: Nikon, OM, Pentax M42 Screw, and Leica SLR lenses can all be adapted.
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The Olympus DSLRs are the most versatile of all in terms of accepting older lenses via adapters. There are adapters for OM, Nikon, Pentax (both screw mount AND bayonet), Leica R and Minolta MD lenses to fit Olympus DSLR cameras. SLR Lens Mount Identification Guide With Oly there's pretty much no wide angles though, even the rare 20mm lenses would be a 40mm, not even considered wide, with the even rarer 15mm only starting to get wide.
I'd say Canon is still king, but Pentax is king if your cabinet is full of K-mount.
I choose pentax colors over canon anyday though... unless it's the 5D or 1D